Bat Detectors

Bats have a fundamental role in natural ecosystems and human economies health. Insectivorous bats are the best natural pest control (studies indicates that normal bats can eat 70% of their weight in insects, value that can reach 100% in pregnant ones); nectar-feeding bats are excellent pollinators, fundamental to several wild or cultivated cultures; fruit-eaters bats are seed dispersers by excellence, restoring vital forests and ecosystems.

In order to cope economic development with nature conservation, impact studies and environmental monitoring have to be undertaken to determine the extent of project-related impacts and define measures to reduce it since early stages of the project until decommissioning.

How do we do it?

To assess impacts from a project, we first need to know what species are using the area and with which intensity. Which species are using the area? Are there any especially sensitive species? Are they using the area all year-round or just for specific periods of time? These are example of questions we need to take in consideration while determining the impact of a project on bats. To do so, we aim to determine the following:

  • Species Richness (meaning: number of species);

  • Activity Index (bat activity per given period of time and/or area);

  • Location and use of roosts within and around the site;

  • Type of utilization of the area by bats.

Data collection techniques and methods

Bats are nocturnal mammals that, in the majority of species, emit ultrasound calls to guide them in the dark, and to detect prey, as well as to communicate. Tracking the conservation status of bat populations through the analysis of abundance and distribution of these calls, has the potential to offer a more efficient alternative to visual sampling methods or evasive methods, such as trapping, in bat monitoring programs. The detection, recording and analysis of bat calls is very useful in the detection of different bat species, since most species have their own call with a specific set of characteristics. Acoustic detection methods are usually of two types: Active or Passive.

Active Detection

Active detection of ultrasounds is conducted with a portable ultrasound detector along vehicle-based transects (ground sections under study) or hand-held at stationary points. The active detection surveys are generally conducted once per season for a full year, and the established transects/points are intended to be representatives of the biotopes (area of uniform environmental conditions providing a living place for a specific assemblage of plants and animals) present at the study area. Environmental variables are also collected during each active survey, such as wind speed and direction, temperature, precipitation, lunar phase, moon visibility and cloud cover (which affects available night sky light).

What is active detection data used for?

What is used for?

After conducting transect/point sampling surveys, the recorded data is analyzed in order to determine spatial use by bat community, as well as to acoustically confirm the presence of bat species that may occur in the area.

Passive Detection

Passive detection of ultrasounds is conducted by means of an automatic ultrasound detector that is left in the field to survey for long periods of time (ranging from 1 week to several years, depending on the project’s specifications). The equipment is scheduled to automatically record calls every night starting 30 min before evening civil twilight and ending 30 min after morning civil twilight.

According to the specific nature of the study, several different locations for detector placement can be used: some detectors can be placed on meteorological masts, or/and in poles, and other can be place at different habitats. In this case, these locations are determined to assure covering most of the important microhabitats and vegetation types present in the area. On the other hand, detectors installed on meteorological masts usually have a microphone installed at rotor height and another one closer to the ground.

What is active detection data used for?

What is used for?

While active monitoring provides a general idea of bat activity throughout the study area, passive monitoring provides much more detailed information on bat activity and species present at the area. The placement of environmental sensors and ultrasound microphones at two different heights on the met mast allows the understanding of the natural variations of bat activity and comparisons of bat activity and diversity, both at rotor height and ground level.

The combination of these two methodologies allows to collect significant data with high level of detail, which can lead us to a deeper investigation and a global understanding of bat activity in the area.

Data analysis and criteria:


Ultrasounds analysis

Bat acoustic monitoring produces large amounts of data impossible to be processed manually. This led to a need for automatic data analysis and bat call identification processes. We then use specific software’ with filters to eliminate all non-bat ultrasounds in the recordings, such as rain, wind, birds and insect sounds and process data to determine bat activity. The filters are cross-validated by selecting a proportion of recordings in each survey and analysing them manually by a specialized technician to make sure the filters are working correctly.